The present invention relates to a slide shoe assembly for a roll in a paper/board machine or a finishing machine, said roll comprising a non-rotating or stationary axle. Around the axle is rotatably mounted a cylindrical roll shell, a clearance formed between its inner surface and said axle being fitted with loading elements operated by a pressurized hydraulic fluid. The loading elements include slide shoes loadable against the inner surface of the roll shell for controlling the distribution of a nip pressure in a nip established with a counter roll.
The invention relates further to a loading shoe for a thin-shelled deflection-compensated roll in a paperboard machine or a finishing machine, said roll comprising a massive stationary roll axle and a thin-walled roll shell mounted rotatably around the roll axle, said loading shoe being fitted in a loading chamber formed along the roll axle and being loadable by means of a hydraulic medium present in the loading chamber towards the inner surface of the shell for bringing the sliding surface of the shoe against the inner surface of the shell, and said deflection-compensated roll establishing a nip with a counter roll.
The invention relates also to a slide shoe assembly for slide bearing of a roll in a paper/board machine or a finishing machine, said assembly comprising a hydrostatic loading shoe, including a piston element fitted in a cylinder boring, as well as a curvilinear slide shoe attached to or integrally included in the outer crown of the piston element and provided with bearing pockets, whereby, by delivering a pressure medium into the cylinder boring below the piston element, the slide shoe is adapted, as a result of a pressure produced by the pressure medium, to bear, through the intermediary of an oil film produced by a lubricating oil delivered into the bearing pockets, against a rotating roll axle to be fitted with a bearing.
The invention relates still further to a hydrostatic loading shoe for a roll in a paper machine, said hydrostatic loading shoe comprising a piston element fitted in a cylinder boring, as well as a curvilinear slide shoe attached to or integrally included in the outer crown of the piston element and provided with bearing pockets, whereby, by delivering a pressure medium into the cylinder boring below the piston element, the slide shoe is adapted, as a result of a pressure Hi produced by the pressure medium, to bear, through the intermediary of an oil film produced by a lubricating oil delivered into the bearing pockets, against a rotating cylindrical surface to be fitted with a bearing.
The use of thin-walled shells, having a shell thickness, e.g. within the range of about 30 to about 60 mm, in deflection-compensated rolls is beneficial, regarding, e.g. the adjustability of the crosswise characteristic profile of a paper web. One problem in such thin-walled shells is an inward deformation of the shell at the nip, which is caused by a nip load and results at the nip in the thinning and even breakdown of a lubricating film between the shell and the loading shoe. In order to overcome this problem as far as a zone- regulated roll is concemed, has proposed a slide shoe assembly, wherein the solid walls of chambers present in the slide shoes are replaced with elastic walls adapting automatically to a deformation of the shell. However, this solution is relatively complicated and expensive.
In the deflection-compensated rolls of a paper machine, the roll shell is normally mounted rotatably on a stationary roll axle in such a way that the roll axle is provided with cylinder borings or the like, which are fitted with pressure-fluid chargeable hydraulic loading elements, used for loading the roll shell usually in the direction of a nip plane, These hydraulic loading elements or loading shoes comprise a piston element fitted in a normal fashion in a cylinder boring present in the roll axle, as well as a slide shoe present at the outer crown of the piston element and bearing against the inner surface of the roll shell. The loading shoe, and particularly its piston element, is often designed in such a way that the piston element itself is cup-shaped and includes a cavity exposed to the action of the pressure of a pressure fluid for loading the slide shoe against the inner surface of the roll shell. It has been a particular problem with loading shoes of this type that the loading pressure existing underneath the shoe tends to lift the slide shoe upward over its mid-section as opposed to its edge zones. Hence, the slide shoe deflects, whereby the contour of its outer surface may become unfavourable relative to the curvature of the inner surface of a roll shell, leading to faults in the operation of a slide shoe and particularly to excessive oil leak through between the slide shoe and the roll shell. At present, attempts have been made to overcome this deflection problem by increasing the thickness of a slide shoe, thus increasing its rigidity along with its thickness. Naturally, this has also increased the mass of a shoe.
Nowadays, the journalling of rolls in paper machines is more and more often carried out by using slide bearings instead of ordinary roller bearings. This is because slide bearings are largely capable of avoiding the problems and restrictions involved in roller bearings. Such hydrostatic slide bearings are equipped with curvilinear slide shoes, which position themselves around the neck of a roll axle for mounting the axle rotatably relative to a bearing block. The slide shoe is secured to a piston element fitted in a cylinder present in the bearing block, the slide shoe being loaded against a journal by supplying a pressure fluid into said cylinder below the piston element. These slide bearings involve a problem similar to what is found in the loading shoes of deflection-compensated rolls, i.e. deflection of the sliding element or sliding surface of a slide bearing. This deflection, or a change in the curvature of a shoe under a pressure load, can be highly detrimental in view of the performance of a bearing At worst, the deflection of a shoe is so significant that, as a result of this deflection no sufficient oil film can be established between the slide shoe and the journal, resulting naturally in a damaged bearing. Earlier attempts have been made to eliminate this problem in such a way that the rigidity of a slide shoe has been increased in a manner similar to what is done in connection with the loading shoes of deflection-compensated rolls.
It is one object of the invention to provide a slide shoe assembly of the above-mentioned type, whereby it is possible to prevent as well as possible the thinning or, in the worst case, the breakdown of an oil film resulting from the deflection of a roll shell.
It is a second object of the present invention to provide an improved loading shoe and a method for eliminating the nip-load induced deformations of a thin-walled deflection-compensated shell in a comparatively simple manner which is applicable in connection of both individually adjustable and zonewise adjustable loading shoes.
It is yet another object of the present invention to provide such a loading shoe, especially a loading shoe fit for supporting the roll shell of a deflection-compensated roll or for fitting a roll with a slide-bearing, wherein changes in the curvature of the shoe under a pressure load are minimized.
According to a first aspect of the invention, a slide shoe assembly for a roll in a paper/board machine or a finishing machine is principally characterized in that the loading element is equipped with means capable of eliminating or compensating for a nip-load induced deflection of the roll shell and/or a deflection of the slide shoe caused by the pressure of a hydraulic fluid, thereby eliminating the harmful effects caused by said deflections on an oil film between the loading shoe and a cylindrical surface supported thereby.
A slide shoe assembly according to another aspect of the invention is characterized in that the unpressurized space comprises a lengthwise slot, extending longitudinally of the roll between opposite sides of the slide shoe and opening at both ends thereof into said clearance.
According to yet another aspect of the invention, a loading shoe for a thin-shelled deflection-compensated roll in a paper/board machine or a finishing machine is characterized there are two or more stabilizing chambers in axial succession on either side of the high-pressure chamber.
According to still another aspect of the invention, a hydrostatic loading shoe for a roll in a paper machine is characterized in that the void space below the slide shoe is established by means of a shaped piece secured to a bottom of the piston-element cavity. The invention according to this aspect is capable of offering certain benefits over the currently available solutions, including as follows. The invention can be exploited for reducing material thicknesses in a shoe and, respectively, for increasing the pressure level of a shoe. Particularly in deflection-compensated rolls, this results in a major advantage in the sense that the possibility of increasing the pressure level has a consequence of increasing the adjustment range of a linear load achievable by the shoes. Respectively, in connection with slide bearing, the height of loading shoes can be reduced, one result of which is, e.g. that the size of bearing assemblies can be reduced. Other benefits and characterizing features of the invention are described in the subsequent detailed specification of the invention.